"We have a smash driver model that takes the HAL and the run time layer and smashes it together and the games on the game binary are ... implement the hardware laid out data that the hardware GPU eats directly. So it's not a HAL layer abstraction and it makes it significantly more efficient. MS also pretty much re-writes ... so basically we completely re-write the driver and smash it together ....[snip who does it, and they're fantastic!] ... and replaces that, and .. pretty much all the firmware in the GPU with MS written firmware and so it's significantly significantly [note: he said it twice!] more efficient than the PC."
He explains they've done this since the first Xbox. I think this basically sums up how the Xbox 1 is able to maintain solid frame rates on it's puny Jaguar cores when the PC needs higher clocks on cores with vastly greater IPC.
I think you are mixing up the CPU and GPU here. The CPU does not really have a "driver" (or what you want to call it in a console setting).